The present invention relates to improvements to capstan tool holders for punching machines.
Capstans of this type comprise a punch holder chuck and a die holder chuck, which are spaced from one another to permit the passage of the plates to be machined. These two chucks are kinematically connected to a rotary drive mechanism in such a way that their respective movements are precisely synchronized, without slipping.
According to a first constructional form, the drive mechanism makes it possible to drive the chucks at high speed during the search of the selected tool and at low speed during the approach of the said tool to the punching station. This drive mechanism comprises a chuck which frees the two synchronized chucks, whilst leaving them coupled to one another when the selected tool has reached the said punching station.
According to a second constructional form, the drive mechanism only has a single high speed which is used during the search of the selected tool. However, it cooperates with brakes acting on the two chucks, in order to slow them down during the above-mentioned approach phase. Moreover, the drive mechanism also has a clutch acting in the manner described hereinbefore.
In both the above constructional forms, each chuck is dependent on a selection device comprising detecting members, such as proximity detectors, microswitches or the like, mounted about the capstan on the fixed frame which supports the latter and distributed in the same way as the tools. The selection device also comprises a cam for actuating the said detection devices, carried by the chuck in question. The appropriately programmed control logic mobilises the detection device which must be actuated by the cam in order to bring the selected tool to the punching station and neutralises the other members, so that when the said detection member is actuated by the said cam it emits a control signal.
Moreover, by means of the above-mentioned selection device, each chuck is made dependent on an indexing device comprising a pin carried by the fixed frame, but radially displaced towards the chuck in question or parallel to the rotation axis of the said chuck so as to penetrate one of the bores made in the periphery of the latter and distributed in the same way as the tools.
The control signal emitted by the selection device has the effect of controlling either the brakes or the change-speed gear of the drive mechanism, disengaging the latter and actuating the indexing pins so that they penetrate the selected bores of the two chucks, in order to precisely immobilise the latter. This is achieved in that each pin and the holes are precisely shaped in complementary manner and in that contact is established between non-deformable and durable metal surfaces thereof.